1. Technical Field
This invention relates to a method and system and the use of a 3-D positioning system, such as but not limited to GPS, Glonass, Galileo, Robotic transit or other means, for monitoring a landfill and landfill material added thereto and undergoing compaction and, in particular, to such a method and system to measure in real time the relative density of the compressed landfill material. Even more particularly, the present invention is directed to a method and system for developing a landfill of substantially optimized density for calculating real density on a periodic basis.
2. Background Art
In a landfill operation, trash and like material is typically spread over a work site in an uncompacted state and then repeatedly traversed by a compaction machine until the material is compressed to a desired degree. Typically, this involves the packing and orientation of solid articles into a more dense and effective arrangement for reducing air voids and like discontinuities. Compaction of material is important in that it provides increased shear strength and density to enable further use of the material in construction operations. In a landfill, maximizing the return on investment is achieved by getting the most material possible into a fixed amount of space.
In packing of most earth material, such as sand or clay, it is possible to model the materials and the compaction process to calculate an equation for achieving the desired density. The equation calculates “y” number of times it is necessary to pack “x” thickness of material. However, this model is only good as long as the material being compacted is uniform in properties, such as shear strength, size distribution of particles, moisture, temperature, composition and other variables and it is placed at a constant thickness accurately. The model is, also, based upon machinery that compacts at constant rates. Yet, two different pieces of compacting machinery, for instance, may possibly have different characteristics, such as whether or not they both vibrate, whether or not the both weigh the same, have the same wheel shape and arrangement, etc. and thus differing compaction efficiencies for differing materials. Clearly, a model for optimum compaction based upon a system using screened sand of uniform moisture and temperature, placed at a uniform thickness on one given day by one machine would be less likely to result in errors in density than a model of material from an unknown source, of unknown strength, unknown moisture, with machines from two different manufacturers on the same site, etc.
In a landfill, or any air space permitted site, the optimum use of the site to place the maximum material into that site is of great economic importance. The designed structure of the landfill requires containing materials to intersect contained materials. Errors in the placement of contained materials may result in less material being placed within the landfill than it is designed for or may result in containment structures that are not of minimum design thickness, slope and grade. Containment and placement of contained materials are normally penecontemporaneous. Currently, the interface zone must be measured frequently to assure that the operators of the contained material moving machinery are indeed placing the material within the permit area.
Compacting operations are largely monitored and controlled intuitively by the machinery operators and supervisors, or by estimating the average characteristics of the material being deposited in the landfill and, then, creating a model that tells the operator to compact the material in the landfill based upon that model. Such an approach may tell the operator to “roll” a “layer” a number of times “n” based upon the model. That is, the compactor may be directed to pass over (i.e., “compact”) a worksite surface contour more than one time, as needed, to further compact (i.e., “density”) the layer of material just added. As such, efforts to electronically provide the operator with detailed information regarding the progress in the compaction effort have been made.
In landfills, a common method used to determine compaction is to survey the surface and set stakes. As compacting machines roll the surface, they re-survey the stakes to determine when the practical point of refusal (the point at which diminishing movement causes one to decide that it is no longer cost effective to attempt to drive the surface down more.) has been reached. This method does not yield real time information over the working surface but instead provides a snapshot of progress.
In one known approach, a plurality of target stakes and an electronic unit for transmitting/receiving electronic signals are positioned about a worksite. Using a surveying-like apparatus, the electronic unit is vertically positioned on a tripod and signals are transmitted to and reflected back from the target stakes. The combination of distance and direction measurements is sufficient to determine the location and elevation of the target points, which data can be electronically stored and/or plotted on a map, converted into X-Y-Z coordinates, and used to generate a contour map. Because landfill unloading trucks and a compactor machine must constantly traverse the worksite, the operator must constantly position/reposition the stakes. This is very labor intensive and may generate an inaccurate cross-section. Critically, this cross-section derived contour map may give an indication of volume, but not the density of the landfill layer.
See also the methods and apparatus disclosed in U.S. Pat. No. 5,493,494 to Henderson and in U.S. Pat. Nos. 5,735,352 and 5,801,967 to Henderson et al.
Illustrative of other efforts are the systems and methods disclosed in U.S. Pat. Nos. 5,471,391 to Gudat et al. and 6,460,006 to Corcoran. According to these references, a global positioning system (GPS) generates, in real time, a contour map of the worksite as well as information relating to the compactor machine. However, these systems do not provide details of density obtained from successive passes of the compactor over the landfill material. They also end up having an operator roll portions of the fill that have already reached the practical point of refusal.
While the recent efforts have advanced the hit or miss approach of the earlier approaches, a simple yet effective method and system for estimating the density of the compacted landfill materials, using conventional apparatus would be desirable.